Abstract: Aims. We observed the $τ$ Boo system with the HARPS-N spectrograph to test
a new observational strategy aimed at jointly studying asteroseismology, the
planetary orbit, and star-planet magnetic interaction. Methods. We collected
high-cadence observations on 11 nearly consecutive nights and for each night
averaged the raw FITS files using a dedicated software. In this way we obtained
spectra with a high signal-to-noise ratio, used to study the variation of the
CaII H&K lines and to have radial velocity values free from stellar
oscillations, without losing the oscillations information. We developed a
dedicated software to build a new custom mask that we used to refine the radial
velocity determination with the HARPS-N pipeline and perform the spectroscopic
analysis. Results. We updated the planetary ephemeris and showed the
acceleration caused by the stellar binary companion. Our results on the stellar
activity variation suggest the presence of a high-latitude plage during the
time span of our observations. The correlation between the chromospheric
activity and the planetary orbital phase remains unclear. Solar-like
oscillations are detected in the radial velocity time series: we estimated
asteroseismic quantities and found that they agree well with theoretical
predictions. Our stellar model yields an age of $0.9\pm0.5$ Gyr for $τ$ Boo
and further constrains the value of the stellar mass to $1.38\pm0.05$
M$_\odot$.